You can't see prior credit card information in the account management section of POL. At the most you get the last four digits, which isn't putting you in any danger. As far as someone not changing it and charging the game off your card goes too, can dispute the charges easily enough and lock it out altogether.

Likewise you could just add a prepaid card to the account before you sell it if you're really worried about security.. It's not even inconvenient to do it that way. >_>